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KVM: arm64: Make active_vmids invalid on vCPU schedule out

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Like ASID allocator, we copy the active_vmids into the
reserved_vmids on a rollover. But it's unlikely that
every CPU will have a vCPU as current task and we may
end up unnecessarily reserving the VMID space.

Hence, set active_vmids to an invalid one when scheduling
out a vCPU.

Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20211122121844.867-5-shameerali.kolothum.thodi@huawei.com
This commit is contained in:
Shameer Kolothum 2021-11-22 12:18:44 +00:00 committed by Marc Zyngier
parent 3248136b36
commit 100b4f092f
3 changed files with 24 additions and 3 deletions
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1
arch/arm64/include/asm/kvm_host.h
View File

@ -694,6 +694,7 @@ extern unsigned int kvm_arm_vmid_bits;
int kvm_arm_vmid_alloc_init(void);
void kvm_arm_vmid_alloc_free(void);
void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid);
void kvm_arm_vmid_clear_active(void);
static inline void kvm_arm_pvtime_vcpu_init(struct kvm_vcpu_arch *vcpu_arch)
{

1
arch/arm64/kvm/arm.c
View File

@ -417,6 +417,7 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
kvm_timer_vcpu_put(vcpu);
kvm_vgic_put(vcpu);
kvm_vcpu_pmu_restore_host(vcpu);
kvm_arm_vmid_clear_active();
vcpu->cpu = -1;
}

23
arch/arm64/kvm/vmid.c
View File

@ -32,6 +32,13 @@ static DEFINE_PER_CPU(u64, reserved_vmids);
#define vmid2idx(vmid) ((vmid) & ~VMID_MASK)
#define idx2vmid(idx) vmid2idx(idx)
/*
* As vmid #0 is always reserved, we will never allocate one
* as below and can be treated as invalid. This is used to
* set the active_vmids on vCPU schedule out.
*/
#define VMID_ACTIVE_INVALID VMID_FIRST_VERSION
#define vmid_gen_match(vmid) \
(!(((vmid) ^ atomic64_read(&vmid_generation)) >> kvm_arm_vmid_bits))
@ -122,6 +129,12 @@ set_vmid:
return vmid;
}
/* Called from vCPU sched out with preemption disabled */
void kvm_arm_vmid_clear_active(void)
{
atomic64_set(this_cpu_ptr(&active_vmids), VMID_ACTIVE_INVALID);
}
void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
{
unsigned long flags;
@ -132,10 +145,16 @@ void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid)
/*
* Please refer comments in check_and_switch_context() in
* arch/arm64/mm/context.c.
*
* Unlike ASID allocator, we set the active_vmids to
* VMID_ACTIVE_INVALID on vCPU schedule out to avoid
* reserving the VMID space needlessly on rollover.
* Hence explicitly check here for a "!= 0" to
* handle the sync with a concurrent rollover.
*/
old_active_vmid = atomic64_read(this_cpu_ptr(&active_vmids));
if (old_active_vmid && vmid_gen_match(vmid) &&
atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_vmids),
if (old_active_vmid != 0 && vmid_gen_match(vmid) &&
0 != atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_vmids),
old_active_vmid, vmid))
return;